1. Field of the Invention
The invention relates to an air cooled brake disc particularly for heavy industrial usage for absorbing relatively short but heavy inputs of energy, or continuous lighter input of energy, whilst maintaining relatively balanced disc temperatures to reduce thermal stresses.
2. Prior Art
Prior art air cooled brake discs usually have a plurality of generally radially disposed, straight cooling passages extending from an inlet opening adjacent the brake shaft to outlets adjacent the periphery of the disc. Such discs are termed "hollow discs" and are commonly cast structures, and thus the design of the cooling structure, ie. passage shape, etc., is dictated to some extent by the method of manufacture as well as thermal stress problems resulting from brake application. Some hollow air cooled brake discs are designed for essentially continuous light braking or intermittent heavier braking with little time for cooling between brake applications. In this type of disc, heat generated by braking is removed by air flowing through the cooling passages and from surrounding air contacting the outer surfaces of the disc.
In some applications discs without air cooling passages, termed "solid discs", are used. In solid discs it is mainly thermal capacity of the material in the disc that is used to absorb the heat generated by braking, that is the mass of disc material is used as a heat sink with minimal removal of heat by air cooling during the application of the brake. Solid brake discs as above are commonly used in applications where the brake is engaged heavily for a relatively short time, and is then disengaged for a relatively long period during which the brake cools in surrounding air where heat from the material in the disc is conducted outwards to outer surfaces where the heat radiates or is lost by convection. This contrasts with removal of heat by intimate contact of a flow of cooling air with large surface areas of the cooling passages in the hollow disc, and for heavy duty applications requiring large discs, mass of the disc becomes unpractical and thermal stresses generated can cause cracking or warping of the disc.